First-principles Study On Electronic Structures And Photocatalytic Performance Of Novel Two-dimensional Materials And Their Heterostructures

Semiconductor photocatalysts can split water to produce hydrogen under the irradiation of visible light,which is considered to be an effective way to solve the current energy shortage and environmental pollution problems.Although many theoretical and experimental studies have shown a large number of photocatalysts,the efficiency of hydrogen production is still relatively low.Recently,some new two-dimensional?2D?materials have exhibited excellent physical and chemical properties,creating new possibilities for enhancing photocatalytic performance.Among them,the construction of heterostructure photocatalyst can enhance the absorption of visible light and reduce the recombination of electrons and holes,greatly improving the photocatalytic performance,which also becomes one of research hotspots in energy technology.In this paper,electronic structure and photocatalytic mechanism of the novel 2D g-C₃N₄/InSe heterostructure,the influence of strain-engineering on the geometric structure and electronic properties of monolayer SiC and the photocatalytic performance of SiC/InSe nanocomposite have been systematically investigated by using first-principles calculations.The main research contents are summarized as follows.The 2D g-C₃N₄/InSe heterostructure is a direct band gap semiconductor and possesses certain stability with its lattice mismatch less than 1.5%and binding energy-1.85 eV.The heterostructure has a gap value of 1.93 eV with a relatively wide visible-light absorption range and an absorption coefficient up to 10⁵ cm^-1.It also exhibits a type-II band alignment and band offsets of conduction band and valence band are 0.74 and 0.78 eV,respectively,indicating that the photo-generated holes are transferred from the InSe layer to the g-C₃N₄layer and vice versa for electrons.Above results prove that electrons and holes are spatially separated.Moreover,the indirect band gap of InSe monolayer prohibits the combination of the photo-generated electrons and holes in g-C₃N₄/InSe.Besides,mobilities of the electron and hole in g-C₃N₄/InSe heterostructure are high up to 10⁴ and 10² cm²V^-1s^-1,respectively.These results all demonstrate that 2D g-C₃N₄/InSe heterostructure has an excellent photocatalytic performance,so it can be regarded as a new photocatalyst.The phonon spectrum and electronic structure of monolayer SiC have been calculated by first-principles calculations.The phonon spectrum result reveals that all phonon frequencies are positive clearly,proving that monolayer SiC is dynamically stable.The band structure displays that SiC is a wide and direct bandgap semiconductor with a GW gap value of 3.73 eV.Furthermore,the effects of uniaxial and biaxial strain on the electronic properties of monolayer SiC have been studied under GGA-PBE function.Monolayer SiC exhibits a transition from direct band gap to indirect band gap by single x-axis compressive strain,single y-axis strain and biaxial compression strain control,while under the single x-axis and biaxial tensile strain,monolayer SiC is still a direct bandgap semiconductor.The gap values are almost reduced under uniaxial strain.From biaxial compressive strain to biaxial tensile strain,the gap values of SiC show a trend from large to small,ranging from 2.86 to 2.11 eV.Based on the monolayer SiC semiconductor,the geometry structure,electronic properties and photocatalytic performance of constructed SiC/InSe nanocomposite have been studied.The calculated lattice mismatch is less than1.3%and binding energy is-4.32 eV,which manifests the heterostructure is stable.The band structure shows that SiC/InSe is an indirect band gap semiconductor with a gap value of 1.78 eV,indicating it has a wide visible-light absorption range and its absorption coefficient reaches 2×10⁵ cm²V^-1s^-1.The photo-generated holes and electrons are located in the SiC and InSe layers,respectively,forming the type-II band alignment,which realizes the spatial separation.In addition,a built-in electric field from InSe to SiC is formed in the heterostructure,which effectively reduces the recombination of electrons and holes.In summary,the designed SiC/InSe heterostructure is beneficial to the enhancement of photocatalytic efficiency.